On Mar 31, 2008, at 5:37 AM, Gianny Damour wrote:
From: David Jencks <[EMAIL PROTECTED]>
1. I think we should try harder to separate the identification of a
constructor parameter as attribute or reference from identifying
its name. So, I think we should use the java6 and xbean
@ParameterName annotations for names and something else for
references if necessary.
It seems to me that xbean only defines a @ParameterNames annotation,
which I think is quite efficient only when the number of parameters
is small. The need of a @ParameterName annotation, targeting a
parameter and not a constructor or method, really emerges when the
number of parameters increases.
If you want, I can add a @ParameterName annotation to xbean-reflect
instead of adding it to geronimo-kernel.
Annotation-wise an @ParameterName annotation would only be useful if
there was an @ParameterNames annotation to act as a wrapper (can't
have more than one annotation of the same name on a target). We
already have an @ParameterNames which accepts String[] so that's sort
of a dead end.
The "extra metadata beyond a name" aspect of constructor and factory
method injection is certainly a tricky one. If you can get by without
needing anything beyond a string, that certainly makes it easier. In
EJB3 we're sort of hosed in that regard as we have @Resource and @EJB,
which is nearly identical to the proposed @Attribute/@Reference
concept; having no polymorphism in annotations makes it impossible to
support both in a list. If we could avoid needing the distinction,
there are advantages.
If we do feel the need to have the distinction, I'd strongly recommend
"reference" being a boolean type on @Attribute or some similar
convention so there's only one annotation type which could be used in
a list. From there "rich" constructor or factory method support could
be as simple as @Attributes(Attribute[]), which I'd recommend be
supportable on a class, constructor or method.
The motivation for supporting it on a class is that there could be
several constructors you might want usable, in which case you might be
motivated to have all the metadata in one spot. Ideally, if you don't
need to explicitly add an annotation for your plain attributes and
only require the annotation when some extra metadata is required,
you'd only need two or three @Attribute annotations on a class.
-David
